This invention relates to ink jet printer devices, and more particularly to the surface treatment of nozzles which are employed in such devices to conduct and eject small droplets of ink for deposit upon record media.
Various types of materials, including glass, are commonly used to form the nozzles for ink jet printer devices. One such material is "Pyrex" glass, which is essentially a glass which contains oxide of boron and has a resultant improved resistance to heat.
Typical glass nozzle configurations are commonly formed using small diameter tube stock, such as 0.020 inch (0.5 mm) I.D. by 0.028 inch O.D. (0.7 mm) tube stock. Forming can be accomplished by heating the glass tube stock and drawing it down at one end to provide a nozzle orifice with a typical diameter of about 2.5-3 mils (0.064 to 0.076 mm). The manner in which such nozzles are made and used is well known in the art.
It has become apparent that the performance of glass nozzles becomes degraded in ink jet printer systems due to the formation and retention of air bubbles within the nozzle conduit. In some cases it has been observed that such air bubbles will adhere to the interior surface area of the nozzle with sufficient tenacity to be immune to substantial efforts to purge them. The presence of air bubbles is a particular problem in drop-on-demand type systems, or systems which operate in a "burst" type mode, where the air bubbles can cause drop velocity and trajectory to significantly vary.
Air bubbles may become present in an ink jet printer system by nucleation of gas entrained in the ink during operation, or by mechanism of ingestion through the nozzle orifice. For example, when an inkfilled nozzle is positioned in a horizontal manner, there is a possibility of air ingestion where the nozzle is physically accelerated, as where the nozzle is moved for printing at different locations with respect to the record media.
Once air bubbles have become present within the ink jet nozzle, it may take varying degrees of effort to remove or purge them from the system. The bubbles have been seen to adhere or "lock" onto the interior surface areas of glass nozzles so tightly that the bubbles remain within the system even as test liquid is forced through the nozzle and ejected through the nozzle orifice as a steady stream.
The small inside geometries of typical glass ink jet nozzles apparently relate nozzle performance to molecular phenomenon. It has been found that the problems of air bubbles in glass ink jet nozzles are a function of wetting properties of the glass interior surface areas or conduit surfaces inside the nozzle. These wetting properties are affected and determined by the presence of impurities and contaminants on the glass surface areas which are involved. Glass which is clean and smooth will be wettable by the ink and not particularly susceptible to adhesion by air bubbles. In contrast, a contaminated glass surface will not be readily wetted by the ink and will provide nucleation points about which air bubbles may form and adhere.
Glass in general is very susceptible to contamination by atmospheric impurities such as dust and other organic and inorganic compounds. Within a short period of time, such as a period of a few minutes, a clean glass surface can become materially contaminated by exposure to the atmosphere. If the surface is the interior surface of a glass ink jet nozzle, the result of the contamination can be a surface area where there is incomplete wetting by the ink, and where air bubbles may form and become attached. An ink jet printer device may thus suffer poor performance due to atmospheric contamination of its glass components.